FIG. 1 is an illustration of example ultrasound transducer 100. Transducer 100 includes, among other things, cable 101 that carries signals between transducer 100 and a processing and control unit (not shown). Transducer 100 also includes body 102 for providing a handle shape for an ultrasound operator to grip transducer 100 when performing an ultrasound examination. Surface 103 of transducer 100 contacts a patient or other subject and includes a plurality of individual transducer elements that transmit and receive acoustic waves during an examination. The processing and control unit controls the beam forming in transducer 100 and also processes the electrical signals produced by the transducer elements as the elements receive reflected acoustic waves during an examination.
FIG. 2 is an exploded view of example components 200 inside transducer 100. As shown, cable 101 is connected to flex circuit 202, and flex circuit 202 is connected to transducer array 201 such that the control and processing unit (not shown) is in electrical communication with transducer array 201. Transducer array 201 includes individual acoustic transducer elements 204, which, in this example, are individually controlled active acoustic elements that produce acoustic waves from electrical stimulation and produce electrical signals in response to receiving reflected acoustic waves. Transducer array 201 is usually fabricated as an “acoustic stack”—one or more ceramic or polymer layers that are metallized on both sides. As explained more fully below, the acoustic stack is cut into a plurality of individual transducer elements. The ceramic or polymer itself is not electrically conductive, but is a piezoelectric material that may be excited by applying a high voltage across its two outer surfaces. The control and processing unit detects minute voltage fluctuations in the signal received from array 201 and performs digital signal processing to produce an image for a human user.
Flex circuit 202 is an intermediary device to connect relatively rigid cable assembly 101 to fragile, small, and minute acoustic elements 204. Flex circuit 202, in this example, is a flexible printed circuit that includes a plurality of signal traces 203 and is similar in some respects to a ribbon. In some examples, flex circuit 202 includes signal traces on a layer of KAPTON™, which is a non-conducting, flexible polymer available from E.I. du Pont de Nemours and Company, that provides flexible support to the traces.
The current art provides for several ways to create an electrical connection between the system electronic circuits in the control and processing unit and the plurality of acoustic elements. Specifically, the prior art provides methods of electrically attaching cable assemblies from the control and processing unit to the acoustic stack itself. One example process includes embedding flex circuit 202 in a block of backing material (not shown), which helps to support both the acoustic stack and the flex circuit 202 during manufacturing and use and also helps to dampen acoustic vibrations in the assembly. A leading edge of flex circuit 202 is visible and exposed at a surface of the backing material so that an electrical connection can be made between flex circuit 202 and the acoustic stack by placing the acoustic stack on the surface so that it contacts flex circuit 202. No soldering is used. The dicing saw operator then cuts through the acoustic stack and the backing material between each of signal traces 203 to create electrically isolated acoustic elements 204. An example method for attaching a backing block and conductive elements to an acoustic stack without soldering is described in U.S. Pat. No. 6,104,126, issued Aug. 15, 2000, the disclosure of which is hereby incorporated herein by reference.
In contrast, current industry standards include soldering flex circuit 202 to the exposed metallized face or edges of the acoustic stack before dicing. A difficulty with both methods is that the exposed leading edge of flex circuit 202 is underneath the acoustic stack, thereby obscuring the signal traces and making the dicing operation more challenging.
FIG. 3 is an illustration of example flex circuit assembly 300. Flex circuit 202 (FIG. 2) includes KAPTON™ layer 303 and a plurality of signal traces 203. Assembly 300 includes backing block 301, which is made of a more rigid, nonconductive material (e.g. acoustic backing material) that surrounds flex circuit 202. Assembly 300 includes surface 304 where a leading edge of flex circuit 202 is visible. In order to guide the dicing saw operator, the assembly line (or the saw operator) scribes backing block 301 with marks 302 (i.e., kerfs) to the edges of block 301. Marks 302 are produced by making shallow cuts in block 301 between the signal traces, thereby transferring a datum feature to the outside of block 301. Marks 302 may then be seen by the saw operator after the acoustic stack is laid down on block 301. Marks 302 indicate spaces between the signal traces where cuts should be made. Marks 302 may be made for each signal trace or may be spaced apart by multiple signal traces in a pattern. In the example of FIG. 3, marks 302 are spaced at every third signal trace.
In both examples above, the dicing cuts and the kerfs are based on the positions of the actual signal traces in the leading edge of flex circuit 202. However, in some applications, discrete signal traces at the leading edges may not be available, making the above-described methods unusable.